Method of manufacturing a steering wheel

ABSTRACT

A method of manufacturing a motor car steering wheel with an external shell made of carbon fibers begins with preparing a pile of sheet materials which is then hot molded to yield respective half-shells with a shape corresponding to that of respective halves of the steering wheel being manufactured. Next comes mechanical flattening of the front surfaces of the two half-shells, followed by mounting of the two half-shells above and under a steering wheel body formed by a metallic core covered by resin. The steering wheel body has lateral profile members which act as fixing supports for the two half-shells.

This is a Divisional of application Ser. No. 09/481,181 filed Jan. 12,2000 now U.S. Pat. No. 6,279,419.

BACKGROUND OF THE INVENTION

The present invention relates to a steering wheel with an external shellmade of carbon fibers and the method of manufacturing the same.

Steering wheels for automobiles are presently made of an internalmetallic core covered by resin and of an external coating and finishingshell, made of various materials, which represents the appearing part ofthe steering wheel.

Among the several known processes for manufacturing motor car steeringwheels is the process comprising providing for formation of twohalf-shells by hot pressing of one or more material sheet inside moldsof suitable shape, subsequent mechanical flattening working of thejunction line of the two half-shells, application of the half-shells ona steering wheel body formed by a metallic core covered by resin andmutual fixing of the two half-shells along said junction line.

Fixing of the two half-shells represents a particularly delicate step ofthe manufacturing process, especially in case of half-shells of smallthickness as those made of carbon fibers.

An object of the present invention is to provide a process of the abovesaid type, which is particularly suitable for manufacturing steeringwheels with a shell of carbon fibers.

According to the invention this object is obtained by a processcomprising preparation of piles of sheet materials, hot molding thereoffor obtaining respective half-shells with a shape corresponding to thatof respective halves of the steering wheel being manufactured,mechanical flattening of the front surfaces of the two half-shells,mounting of the two half-shells above and under a steering wheel bodyformed by a metallic core covered by resin, characterized in that saidsteering wheel body is previously provided with lateral profile membersadapted for acting as fixing supports for the two half-shells.

Fixing of the half-shells is preferably obtained by gluing of theinternal surface of the half-shells on the external surface of thelateral profile members, suitably complementarily shaped.

It has been possible to verify that in this way a very strong structuralassembling is obtained which is able to resist all the aging and safetytest required by the automobile manufacturers.

BRIEF DESCRIPTION OF THE INVENTION

The features of the present invention will be made more evident by thefollowing detailed description of an embodiment thereof which isillustrated by non-limiting way in the accompanying drawings, in which:

FIG. 1 shows, partly in view and partly in section, a typical steeringwheel;

FIG. 2 schematically shows several steps of the manufacturing processaccording to the present invention;

FIG. 3 shows a partial perspective representation of a half-shell afterthe hot molding step and the subsequent flattening step and before theprovision of the coupling teeth;

FIG. 4 shows in perspective view, just before the final assembling ofthe two half-shells, a portion of a steering wheel manufactured by theprocess according to the invention; and

FIG. 5 shows the same steering wheel in cross-section, in assembledcondition.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, a typical steering wheel for an automobile iscomposed by a central part or hub part 1, a plurality of radial spokes 2and an external rim 3.

According to the present technology the external rim 3 and the spokes 2consist of an internal metallic core 4 covered by resin 5 and anexternal coating and finishing shell, in its turn formed by twohalf-shells 6 superimposed to each other and joined together.

The two half-shells 6 are manufactured by using the technologyschematically illustrated in FIG. 2, steps a-d.

More precisely, the forming step provides for hot molding of a pile ofsheet materials, globally designated with 7 in FIG. 2, step a, inside ametal mold 8 with a cavity 9 of suitable shape, on which a cover 10 witha protrusion 10 of complementary shape with respect to the cavity 9 issuperimposed.

The pile 7 may be composed by sheets of various thickness so as toprovide a total thickness of the half-shell which is comprised between1.0 and 2.0 mm.

The single sheets are made of carbon fibers combined with glass fibersor aramidic fibers or a combination of said fibers.

The above mentioned fibers are impregnated with specific resins which atthe end of the cycle are able to grant structural rigidity to thehalf-shell assembly. The resins used for impregnating the fibers can beof various natures, for example epoxy, polyester, and polyurethane. Theimpregnation of the fibers may be carried out both before the use, bymeans of specific machines which dip the fabric into the resin accordinga specific process, and during the half-shell molding step, by smearing,injection or other dispensing systems which allow impregnation of thefibers inside the mold.

The molding time depends on the temperature being used and is comprisedbetween 1 and 3.5 minutes. The mold temperature, for an optimal process,is comprised between 70° C. and 150° C. The molding pressure requiredfor a correct catalysis of the resins is 0.7 bar.

The half-shell obtained at the end of the molding operation isillustrated in FIG. 2, step b, and comprises a curved central part 12and two lateral fins 13. The latter are then removed by mechanicalflattening working, step c of FIG. 2. The half-shell is then as shown inFIG. 3.

Two half-shells obtained in this way are then subjected to a painting,step d of FIG. 2, and provided with glue 14 on their internal surface,step e of FIG. 2. It is possible to use glues of several kinds, whichhave structural functions, belonging to epoxy, polyurethane andmethacrylate families.

Meanwhile, a steering wheel body 15 (formed by the metallic core 4 andthe resin covering 5 as previously said with reference to FIG. 1) hasseparately been prepared, to which two symmetrical lateral profilemembers 16 are applied, for example by clawing, each of which i.5 formedby two lateral flanges 17 with internal surface complementary to theexternal surface of the steering wheel body 15 and external surfacecomplementary to the internal surface of the two half-shells and by anintermediate rib 18 adapted for operating as abutment shoulder for thefront surfaces 19 of the two half-shells. The lateral profile members16, lateral flanges, and the ribs 18 may be made of metal, such asaluminum, steel, titanium, magnesium, etc., or may be a syntheticmaterial such as thermoplastics (ABS, PA, PP, etc.). The rib 18 may beexposed as shown in FIG. 5, being visible after assembling the shellsover the steering wheel grip, or may be hidden after assembly. Theexternal surfaces of the flanges 17 are smeared with suitable glue, ofcourse of the same type as the glue 14.

The two half-shells 6 are put one above and the other under the steeringwheel body 15 with the lateral profile members 16, step f of FIG. 2, andfixed by gluing because of the glue previously applied to the samehalf-shells and to the lateral profile members 16.

The assembly obtained in this way, step g of FIG. 2, may leave a portionof the lateral profile members 16 at sight or hidden them completely.

The painting operation may be carried out after the final assemblingrather than on the single half-shells.

It is to be noted that the steering wheel body 18 is preferably providedwith two diametrically opposite grooves 20 which serve for compensatingthe thermal expansions of the resin 5.

The assembly of the two half-shells 6 and the steering wheel body 15with the lateral profile members 16 is shown in perspective view, justbefore the final assembling, in FIG. 4.

The same assembly is shown in cross-section, with assembling beingended, in FIG. 5.

It is to be understood that while the preferred embodiment of thepresent invention has been described, various changes and modificationsmay be made by those skilled in the art without departing from the scopeof the invention as set forth in the claims.

We claim:
 1. A method of manufacturing a steering wheel with an externalshell made of carbon fibers, which comprises: preparing a pile of sheetmaterials; hot molding the pile for obtaining respective half-shellswith a shape corresponding to that of respective halves of the steeringwheel being manufactured, said shape comprising a curved central partand two lateral fins; mechanical flattening of exterior surfaces of thetwo half-shells by removing the lateral fins; providing a steering wheelbody with lateral profile members, each lateral profile member havingtwo lateral flanges arranged at a side of the steering wheel body and anintermediate rib, said lateral profile members configured to mate withand support circumferentially extending edges of the curved centralparts of the two half shells; and mounting the two half-shells above andunder the steering wheel body.
 2. A method of manufacturing a steeringwheel according to claim 1, wherein the mounting of the two half-shellscomprises gluing an internal surface of the half-shells on an externalsurface of the lateral profile members, which is complementarily shaped.3. A method of manufacturing a steering wheel according to claim 1,wherein said sheet materials comprise carbon fibers and glass fibers. 4.A method of manufacturing a steering wheel according to claim 1, whereinsaid sheet materials comprise carbon fibers and aramidic fibers.
 5. Amethod of manufacturing a steering wheel according to claim 1, whereinsaid sheet materials comprise carbon fibers, glass fibers and aramidicfibers.
 6. A method of manufacturing a steering wheel according to claim3, wherein said fibers are impregnated by resin.
 7. A method ofmanufacturing a steering wheel according to claim 4, wherein said fibersare impregnated by resin.
 8. A method of manufacturing a steering wheelaccording to claim 5, wherein said fibers are impregnated by resin.
 9. Amethod of manufacturing a steering wheel according to claim 1, whereinsaid hot molding is carried out at a temperature between 70° C. and 150°C.
 10. A method of manufacturing a steering wheel according to claim 1,wherein said hot molding is carried out for a time between 1 and 3.5minutes.
 11. A method of manufacturing a steering wheel according toclaim 1, wherein said hot molding is carried out at a pressure of atleast 0.7 bar.